Gallium-67 citrate scans are frequently used to detect the presence of pulmonary inflammatory disease in AIDS patients. Increased pulmonary uptake is very sensitive, although not specific, for PCP in these patients. Because some patients with AIDS and PCP respond poorly to therapy and require several bronchoscopies to assess therapeutic response, we are using Gallium scan assessments to correlate with lung histology in patients with PCP in order to further evaluate diagnostic sensitivity and prognostic significance. All patients with AIDS and documented PCP have Gallium scans that are read blindly by a nuclear radiologist and these results are correlated with initial and follow-up histopathology sections obtained by transbronchial biopsies. In patients who also had a follow-up Gallium scan after appropriate anti-PCP therapy, the changes in Gallium scans are correlated with histologic clearance or persistence of PCP. Preliminary results seem to indicate: 1. A wide scatter in initial Gallium scores in AIDS patients with PCP. 2. Failure to improve Gallium scores following treatment is associated with PCP persistence. 3. Comparison of scan scores pre- and post- therapy may predict clearance of PCP.